Recently Hall effect position sensors, in which permanent magnets and Hall elements are combined, are applied in various sorts of mechanical apparatuses, electric/electronic apparatuses, automation apparatuses, etc. In such a Hall effect type position sensor a magnetic field generating section is constructed by mounting permanent magnets on an examined body, whose position is to be detected and a magnetic field detecting section consisting of a Hall element is constructed so as to be slidable relatively with respect to the magnetic field generating section. The position of the examined body is detected owing to the fact that the Hall element in the magnetic field detecting section detects the magnetic field generated by the magnetic field generating section by Hall effect, when the magnetic field generating section and the magnetic field detecting section are close to each other by generating an electric signal.
Hall effect is observed by a Hall element that consists of a semiconductor thin film 20 such as InSb. When a current I is made to flow in a certain direction through this semiconductor thin film 20 and a magnetic field H is applied to the film in a direction perpendicular to the direction of the current I, as indicated in FIG. 6, a Hall voltage Vh is generated in a direction perpendicular to both the current I and the magnetic field H. The Hall voltage Vh is proportional to the product of the current I and the magnetic field. Thus, it is possible to generate a Hall voltage Vh, i.e. electric signal, corresponding to the intensity of the magnetic field, by application of the magnetic field to the Hall element. This makes it possible to detect the position of the examined body subject to necessary control operations such as stop of the examined body at that position, etc. Since a Hall effect position sensor constructed by using such a Hall element for the magnetic field detecting section has an advantage that it has a high reliability, because it has no mechanical contacts such as microswitches, etc. and that it works without contact with the examined body, it is applied in a widely extended field.
A prior art example of such a Hall effect type position sensor there is disclosed in JP Utility Model-A-Hei 1-81837. In this construction, as illustrated in FIG. 7, the magnetic field generating section 24 is constructed by a magnet 23 consisting of two magnetic elements 21 and 22 magnetized partially in different directions. This magnetic field generating section 24 and a magnetic field detecting section 25 consisting of a Hall element are slid relatively in a magnetic flux direction 26 with an operation distance h.
Another prior art Hall element disclosed in JP Utility Model-A-Hei 1-100348. In this construction, illustrated in FIG. 8, a permanent magnet 32 is mounted on a piston 31 the position of which is to be detected. More specifically two magnetic bodies 33 are mounted on the two ends on the piston in the slide direction to construct the magnetic field generating section 34. The magnetic field detecting section 37 consisting of a Hall element 36 is relatively slid with respect to the magnetic field generating section 34 through a cylinder tube 35. In each of these prior art examples the Hall voltage Vh outputted by the Hall element is amplified by an amplifier and further compared with a reference value by a comparator. In this way a switching operation is effected and a control signal is outputted to the examined body.
These prior art Hall effect type position sensors have a problem in that deviations of the detection position in the slide direction can become significant in situations where the operational distance between the magnetic field generating section and the magnetic field detecting section varies.
For example, in the prior art example indicated in FIG. 7, since variations in the operation distance h between the magnetic field generating section 24 and the magnetic field detecting section 25 sometimes cannot be avoided, when the distance h varies, detection precision is lowered, because the detection position in the slide direction 26 deviates.